Structural material



June 5, 1945. I D, HNLAYSON A| 2,377,335

STRUCTURAL MATERIAL File d Sept. 4, 1941 "VI/EN TORS lw/Aluysolv fic-HALE I .9 ATTORNE YS Patented June 5, 1945 don, near Derby, England,assignors to Celanese Corporation of America, a corporation of DelawareApplication September 4, 1941, Serial No. 409,520

, In Great Britain September 28, 1940 7 Claims. (Cl. 154-43) Thisinvention relates to structural materials and particularly to materialsof a composite character. 1

According to the invention stress-resistin members having such a size orshape of crosssectional area as to be rigid or relatively rigid comprisea fabric base embedded in plastic ma-- terial, the fabric comprising atleast one set of heavy parallel yarns lying close to each other. Theparallel yarns may be bound to each other by interlaced lighter threadsthat not only hold the heavy yarns parallel and close to each other butpermit them to lie straight, giving a woven structure in which anywaviness arising from the interlacing is substantially confined to thelight binding threads. The close packing of the heavy yarns coupled withthe straight formation of those yarns provides a base fabric in whichthe maximum tensile strength is obtained; and, with the rigidityimparted by embedding the yarns in plasticmaterial (which should havelow elasticity), a rigid or relatively rigid structure can be formedsuitable for a variety of uses, such as ties, beams, torsional members,and like members having a length that is substantial as compared withtheir cross-sectional dimensions. Where the use of any such member mightproduce a tendency to splitting along lines parallel to the heavy yarns,it may be advantageous to employ fighter binding threads as indicatedabove. Such a tendency may, however, be resisted by providin a morelaborate fabric structure, for example, one in which one or more othersets of heavy parallel yarns are provided to give layers in which theheavy yarns of one layer cross those of another layer at a. substantialangle, e. g., at rightangles. Provision of the kind just mentioned mayalso be desirable where the structural material is intended to be usedas a. strut,

It is particularly advantageous to form the' base fabric from yarns ofexceptional tensile strength. Outstanding yarns in this respect arecontinuous filament yarns of regenerated cellulose produced, forexample, by the complete sa- 7 'ponification of yarns of celluloseacetate or other plete saponification of such materials may even furtherincrease tenacity. Stretched, or stretched and saponified filaments ofthis character have a relatively low extensibility, e. g., about 6%, andfor some purposes this is an advantage in producing relatively rigidstructural members of the kind with which the invention is concerned.The extensibility may,,however, be improved by subjecting the yarns,after stretching, to a shrinking treatment; for example, strong yarns ofcellulose acetate may be shrunk by treatment in a bath containingmethylene dichloride or ethylene dichloride diluted. with benzene ortoluene. The shrinking is accompanied by some loss of tenacity but canbe so controlled that the tenacity still remains high, e. g., between 2and 4 or 5 grams per denier. Other high tenacity yarns suitable for useaccording to the invention can also be made by wet-spinning organicesters of cellulose under such conditions that the materials arestretched considerably, for example, by several hundreds per cent oftheir extruded length. In this case also, the-original tenacity of thematerials ca still further be increased by saponification. Again,regenerated cellulosic yarns of high tenacity can also be made directlyby spinnin solutions of viscose or cuprammonium cellulose under suitableconditions, for example, under such conditions that a considerablestretch is efiected.

Among other materials of which the heavy yarns may be composed arecellulose ether materials that in their manufacture have been subjectedto similar processes to those referred to above for ensuring hightenacity, and yarns of the so-called super-polyamides and like linearpolymers, e. g., those containing in their structural unit ester groupsor anhydride groups.

per denier can be obtained in this way and com- Natural silk yarns .arealso suitable for the production of base fabrics of high tenacity.

By the use of high tenacity materials relatively rigid compositestructural materials of high strength can be obtained, which may be usedin -substitution for metallic structural elements, and,

in many cases, enable a saving in weight to be ob tained. Where,however, high strength is not of the greatest consideration, othertextile materials may be used for the heavy yarns, e..g., cotton, wool,jute, hemp and linen, and likewise staple fibre yarns produced fromcontinuous filaments of the character already mentioned, provided thatthe close packed parallel arrangement of the heavy yarns is adhered to.Where lighter binding threads are employed in the fabric structuretohold the heavy yarn close toeach other it is generally advantageous toemploy as these binding threads the stronger types of textile materialsreferred to above in order to keep the relative proportion of bindingthread to heavy yarn as low as possible.

Various forms of plastic material may be used for embedding the basefabric. In order to provide the necessary rigidity highly elasticplastic materials should be avoided. Substances of thermoplasticcharactermay be used, for example, cellulose esters and ethers, e. g.,cellulose acetate, cellulose acetate-propionate, celluloseacetatebutyrate, cellulose acetate-stearate, celluloseacetate-palmitate, cellulose nitrate, cellulose nitrate-acetate, ethylcellulose, benzyl cellulose and ethyl cellulose acetate; and ofpolymerised unsaturated artificial filamentor film-forming substances,for example, polymethyl acrylate, polyethyl acrylate, polymethylmethacrylate, po yvinyl esters and ethers, synthetic resins of thepolystyrene class of co-polymers of one or more of such polymerisedunsaturated compounds. It is advantageous that the plastic materialshould have a relatively high melting point and from this point of viewsimple polymerised vinyl esters,

. for example, polyvinyl acetate and polyvinyl chloride are lesssatisfactory than co-polymers of these esters with unsaturated compoundsof the acrylic series. Cellulose nitrate should not be used where itsinflammable nature might be a disadvantage.

Thermosetting plastics may also be used, for example the syntheticresins obtained by condensation of an aldehyde such as formaldehyde withurea or like acting nitrogenous substances, for example, thioureas,guanidine or dicyandiamide, or with a phenolic compound, for example,phenol m-cresol or 3:5 xylenol. Other plastics such as casein and soyabean protein plastics may likewise be employed.

The plastic may be, applied to a base fabric already shaped tocorrespond to the shape of the structural element desired or the plasticmay be incorporated in-the fabric prior to, or during a preliminaryshaping of the fabric. In either case a moulding operation is generallydesirable to bring about the final shaping of the element,especiallywhere smooth external surfaces are desired. A simple form oflight structural element according to the invention is a plain rodhaving as its basis a cord woven or braided from a number of heavy yarnsheld together :by a light binding thread. Such a cord may for exampleconsist of a number of heavy, parallel core yarns surrounded by a sheathof similar yarns woven together by a single light weft thread. The cordis impregnated with' plastic material and finally moulded into rigidform by the application of heat and pressure. The amount of plasticmaterial may be such as just to permit the rod to have a smooth surfaceafter moulding or, if desired, additional (ill plastic material may beapplied externally of the Structural elements of other cross-sectionsmay be formed by suitably shaping base fabrics prior to embedding themin the plastic material; for example, a ribbon or tube of base fabricmay be folded lengthwise into the form of an L, U, T, or H for insertioninto a correspondingly shaped mould. In the case of such sections as T'sor H's,

stitching may be employed to impart strength I where one portion of thesection branches from another.

Composite elements of the kind described may be pierced or drilled forattachment to each other or to other elements of any structure in whichthey are incorporated. It is desirable, however, to ensure that underthe stress to be withstood, splitting between the heavy yarns does notarise. By reason of the method employed for attaching the elements,suitable reinforcement such as a whipping which may be fltted before thefinal moulding or the application of a ferrule may be employed. For theproduction of time members, however, strips or flattened tubes of fabricmay be wound round a pair of pins spaced to correspond with the desiredpositions of attachment holes at the two ends of the element and thefree ends of the strip or tube may be secured by stitching or whippingprior to moulding, the element as it leaves the'mould already havingattachment holes provided in the positions determined by the pills.

The moulded elements need not have the same cross-section throughouttheir length. For example, the base fabric may be thickened, especiallyat the ends or other parts where provision is to be made for attachmentto other members. Thus, in the case of tubular elements, the end of thetubular base fabric may be folded back on itself. The elements may alsobe flattened or thickened during the moulding operation. Metal insertsorother pieces may be secured in or on to the fabric/plastic structure bythe moulding operation. For example, eyes, bushes, or ferrules may bemoulded in place.

As already stated, plastic material may be incorporated into the fabricstructure prior to the final moulding in which the structure becomesrigidly embedded in the plastic material. In the case of thermosettingresins for example, the base fabric may be impregnated with an aqueoussolution of the resin components so that on the subsequent applicationof heat and pressure in the moulding operation the condensation of thesynthetic resin is completed within the fabric. It is generallyadvisable, however, to apply moulding powder externally of the basefabric in order to produce a smooth surface on the element. Wherethermoplastic embedding materials are employed, e. g., celluloseacetate, impregnation of the base fabric may be assisted byincorporating cellulose acetate yarns in the 'fabric structure. By theapplication of heat and pressure either in the preliminary shaping ofthe base fabric or in thefinalmouldingthecelluloseacetateyarnsbecomeplastic and bring about the adhesion of the non-thermoplastic yarns inthe fabric, aided if necessary by a plasticiser in the cellulose acetatethreads or by the application to the threads or the woven fabric of aplasticiser, solvent or latent solvent causes the cellulose acetatethreads to fuse.

The weight of the heavy threads will depend somewhat on the type ofelement to be constructed and in the case of tubular or otherthin-walled sections, on the thickness of the walls. In general,however, heavy yarns of say 2,500 or 5,000 denier are convenient; forthe lighter binding threads a denier of about 275 maybe employed.

Various forms of members according to the invention will now bedescribed with reference to the accompanying drawing, in which Fig. 1shows a woven sheath surrounding a number of core yarns all embedded inplastic material; I 4

Fig. 2 shows a tubular fabric embedded in plastic material to form atubular member;

Fig. 3 shows the formation of another kind of tubular member;

Fig. 4 shows a member similar to Fig. 1 fitted with a ferrule;

Figs. 5 and 6 are front and side elevations of the end of a memberfitted with a perforated ferrule;

Figs. '7, 8 and 9 show stages in the manufacture of an eyeletted member;

Figs. 10, 11, 12 and 13 are cross-sections of different types oflight-sectioned members; and

Fig, 14 is a cross-sectional view showing the application of a coredmember to the reinforcement of a laminated fabric sheet.

In Fig. 1, heavy yarns I are woven with light threads 2 to form a sheathsurrounding heavy core yarns 3. The heavy yarns I, 3, may be 3/3/5230denier yarn produced by stretching times in wet steam) and saponifyingcellular acetate continuous-filament yarn. The light threads 2 may be ofsimilar material of 275 denier. The solid cord thus formed is embeddedin plastic material 4, this material being shown stripped from the upperhalf of the figure. The plastic.

material impregnates the whole of the cord assembly so as to addsubstantial rigidity to the strong structure formed by the cord elementsthemselves. For example, the cord may be impregnated with liquidurea-formaldehyde before being subjected to a moulding operation in acylindricalmould of circular section and having a length appropriate tothat of the cylindrical member to be formed. In general, the amount ofplastic material should be just sufllcient to impart a smooth surface tothe cord, the thickness being somewhat exaggerated in Fig. 1.

In Fig. 2, a woven tube 5 similar to the sheath formed by the yarns Iand threads 2 of Fig. 1 is embedded in plastic material 6, the mouldingoperation being efiected after the impregnated tube has been inserted ona mandrel closely fitting the bore 'l of the tube.

In Fig. 3, strips 8 of fabric comprising heavy yarns 9 lightly woventogether with threads [0 are wound helically on'a mandrel II to form aninner layer covered by a similar layer formed by strips l2 woundhelically in the opposite direction. The assembly is embedded in plasticmaterial l3 by the use of a cylindrical mould as described withreference to the production of the member shown in Fig, 1.

Fig. 4 shows a rod-like member ll of the type shown in Fig. 1, butfitted with a metal ferrule I! which may provide for the anchoring ofthe member ll. Thus, the outside of the ferrule may be tapered asindicated at IS, the larger end of the ferrule being at the free end ofthe member.

The ferrule can thus be threaded through a correspondingly tapered holein some member to which the member I 4 is to be attached. Aferrule ofthis kind may also be externally screwed to provide a fixing; it maylikewise be drilled similarly to the ferrule shown in Figs. 5 and 6. Toprovide for a firm connection between the member I4 and the ferrule l5the end of the woven tubular sheath I! may be turned back on itself,asindicated at 18, so as tofill the taper bore of the ferrule. When theferrule is moulded in position the setting of the plastic material inthe portion of the braided cord lying within the. ferrule produces anenlarged end that resists any tendency of the ferrule to pull away fromthe end of the member under tension. The surface IQ of the plasticmaterial may run smoothly into the surface of the ferrule.

The ferrule 20 of Figures 5 and 6 is flattened and pierced within a hole2| which enables the member 22 fitted with the ferrule to be used as atension member with a pin-joint connection to another member generallyindicated at 23.

Fig. 7 shows the first stage in the building up of a tension member froma length 24 of heavy yarn fabric which may either be formed byflattening a tube of the kind used in forming the member shown in Fig. 2or a strip or tape of the kind shown in Fig. 3. The length 24 is woundover a pair of eyelets 25 and the parallel portions of the lengtharesewn or whipped, as indicated in Fig. 8. The assembly, including theeyelets, is placed in a mould diagrammatically indicated at 26, in whichthe fabric layers and the eyelets are embedded in plastic material toproduce a tension member, the eyelets of which provide for readyattachment. A moulded tension member of this kind is shown in Fig. 9; inthis case, however, pear-shaped eyelets 21 have been used.

In Figs. 10-13 is a tube of fabric of suitable diameter has beenflattened to form a double layer of fabric and manipulated into varioussections suitable for light compression members. The double layers 28are held together by stitching 29 before placing the fabric in the mouldin which the plastic material 30 is set.

Fig. 14 shows the application of a stress-resisting member, according tothe invention, as the reinforcement of a fabricskln, e. g., of the typedescribed in British No. 514,442. The skin 3| comprises layers 32 ofwoven fabric each consisting of a set of heavy parallel yarns bound toeach other by light threads that permit the heavy yarns to lie straight,the waviness arising from the woven structure being substantiallyconfined to the light binding threads. The heavy yarns in adjacentlayers cross one another at a sub-' stantial angle, e. g., atright-angles. The layers 32 are assembled over a mould 33 and suitablyimpregnated with plastic material. To provide for the reinforcement ofthe -skin the mould is provided with a groove 34' into which is inserteda braided cord of the kind described. in Fig. 1, the cord comprising anumber of heavy core yarns 35 and one or morewoven sheaths 36 to providefor thefirm attachment of the reinforcement to the skin 3|. One or morelayers 36 of fabric, similar to that used for the layers 32,are

laid in the groove 3| prior to the insertion of the reinforcing cord,the layers 21 extending over the surface of the mould 33' for somedistance on each side of the groove 34. Recesses 38 may be provided toaccommodate the layers 31 and enable the outer surface of the skin 3| tohave a smooth uninterrupted curvature. The reinforcing cord may besuitably shaped to fit closely into the groove. When heat and pressureis applied to the assembly of fabric and cord on the mould 33, theplastic material with which the fabric and cord is impregnated welds thelayers 32 into a.solid skin and also welds the reinforcement to the skinto provide a structure capable of withstanding substantial tension andtearing stresses, and also having considerable rigidity arising from thelow-density of the material (e. g., 1.10 to 1.15) as well as from thestifiening imparted by the reinforcing rib.

Having described our invention, what we desire to secure by LettersPatent is:

l. A stress-resisting member having a crosssection enabling it to havesubstantial lateral rigidity, said member comprising a basis of textileyarns embedded in plastic material of low elasticity, the textile yarnscomprising at least one set of parallel yarns lying close to one anotherand containing artificial filaments that have been stretched while in asoftened condition so as to increase their tenacity and reduce theirelasticity.

2. A stress-resisting member having a crosssection enabling it to havesubstantial lateral rigidity, said member comprising a basis of textileyarns embedded in plastic material of low elasticity, the textile yarnscomprising at least one set of relatively heavy parallel yarns boundclose to each other by being interlaced with relatively light yarns towhich the waviness arising from the interlacing is substantiallyconfined, said relatively heavy yarns containing artificial filamentsthat have been stretched while in a softened condition so as to increasetheir tenacity 40 and reduce their elasticity.

3. A stress-resisting member having a crosssection enabling it to havesubstantial lateral rigidity, said member comprising a basis of tex- 4.A stress-resisting member having a crosssection enabling it to havesubstantial lateral rigidity, said member comprising a basis of textileyarns embedded in thermosetting material 01 low elasticity, the textileyarns comprising at' least one set of parallel yarns lying close to oneanother and containing artificial filaments that have been stretchedwhile in a softened condition so as to increase their tenacity andreduce their elasticity.

5. A stress-resisting member having a crosssection enabling it to havesubstantial lateral rigidity, said member comprising a basis of textileyarns embedded in plastic material of low elasticity, the textile yarnscomprising at least one set of parallel yarns lying close to one anotherand containing artificial filaments of an organic ester of cellulosethat have been stretched while in a softened condition and thensaponified so as to increase their tenacity and reduce their elasticity.

6. A stress-resisting member having a crosssection enabling it to havesubstantial lateral rigidity, said member comprising a basis of textileyarns embedded in thermoplastic material of low elasticity, the textileyarns comprising at least one set of relatively heavy parallel yarnsbound close to each other by being interlaced with relatively lightyarns to which the waviness arising from the interlacing issubstantially confined, said relatively heavy yarns containing artitileyarns embedded in thermoplastic material of low elasticity, the textileyarns comprising at least one set of parallel yarns lying close tooneanother and containing artificial filaments that have been stretchedwhile in a softened condition so as to increase their tenacity andreduce their elasticity.

ficial filaments of a cellulose ester that have been stretched while ina softened condition and then saponified so as to increase theirtenacity and reduce their elasticity. V

7. A stress-resisting member having a crosssection enabling it to havesubstantial lateral rigidity, said member comprising a basis of textileyarns embedded in thermosetting material of low elasticity, the textileyarns comprising at least one set of relatively heavy parallel yarnsbound close to each other by being interlaced with relatively lightyarns to which the waviness arising from the interlacing issubstantially confined, said relatively heavy yarns containingartificial filaments of a cellulose ester that have been stretched whilein a softened condition and then saponified so as to increase theirtenacity and reduce their elasticity,

DONALD FINLAYSON. FRANK CORBYN HALE.

